The present invention relates to an adjustable radial piston machine, especially a pump or motor, and, more particularly, to an adjustable radial piston machine comprising a housing having an interior space, a drive mechanism arranged in the interior space and comprising a rotor coupled nonrotatably to a drive shaft or driven shaft outside the housing and provided with a plurality of radially arranged cylinders and working pistons movable in the respective cylinders, a stationary control pivot on which the rotor is rotatably mounted and which is provided with at least one feed duct and/or at least one outlet duct opening into respective control cavities, a bearing ring surrounding the rotor on which the working pistons bear and an adjusting device with which the bearing ring cooperates for adjustment of the operation of the radial piston machine.
A radial piston machine of this type is for example described in German Patent Application DE 41 43 152.9 A1. This radial piston machine has a drive mechanism, which is formed by a rotatably mounted rotor including radially arranged working cylinders. Pistons are guided movably in the working cylinders, which bear on a bearing or piston ring, which surrounds the rotor. The bearing ring is movable as a whole in a straight line relative to the housing for adjustment of the radial piston machine and cooperates with a hydraulic piston-cylinder device for that purpose. The eccentricity present between the bearing ring and the rotor is appropriately adjusted by an appropriate control of the hydraulic piston-cylinder device and thus the operating parameters of the radial piston machine are changed.
The disadvantage to this prior art arrangement is that the hydraulic forces on the rotor produced by the operating cylinders during operation of the radial piston are not balanced. Because of that the rotor bearings are loaded with frictional forces which impair the mechanical efficiency of the radial piston machine. Moreover the frictional forces lead to heating and/or to wear which in the extreme case can lead to seizing and/or to mechanical destruction of the drive mechanism components.